Method and device for producing a microlens

ABSTRACT

This invention relates to a method for producing a microlens with a carrier wafer, in which a lens in one opening of the carrier wafer is molded into the carrier wafer by stamping of the lens and to a corresponding device for executing the method and to a microlens which has been produced using the method. Furthermore the invention relates to a device for producing a microlens as well as a microlens.

FIELD OF THE INVENTION

This invention relates to a microlens, a method for producing amicrolens and a device for producing a microlens.

BACKGROUND OF THE INVENTION

Primarily microlenses are used for devices which require an opticalfocusing means, such as for example cameras and mobile phones. As aresult of miniaturization pressure, the functional components arebecoming increasingly smaller; this also applies to microlenses of thegeneric type. The further the microlenses are to be miniaturized, themore difficult their optically correct production becomes because at thesame time there is enormous cost pressure for microlenses to be ideallyproduced in large-scale production.

In the prior art microlenses are produced on a carrier substrate byvarious production methods, as shown for example in U.S. Pat. No.6,846,137 B1, U.S. Pat. No. 5,324,623, U.S. Pat. No. 5,853,960 and U.S.Pat. No. 5,871,888. It is common to all the aforementioned methods thata certain thickness is necessary in principle and the light which passesthrough the microlens must pass through not only the lens, but also thecarrier substrate.

As a result of the simultaneously required high quality and the demandsfor higher resolution with simultaneously high brilliance, which dependsamong others on the thickness and the number of optics along the opticalaxis, therefore the beam path, further optimization of the microlensesaccording to the prior art is desirable.

Moreover there is a requirement for radiant efficiency which is as highas possible and which is decisive especially for micro optics systems,since the image sensor occupies a generally very small area on whichlight is incident.

U.S. Pat. No. 6,049,430 shows a lens which has been inserted in anopening of a carrier substrate, and the production process shown in FIG.2 requires a plurality of steps and is therefore complex and due to theproduction accuracies which can be attained here would be too inaccuratefor the aforementioned requirements. The plurality of materials to beused is also a disadvantage.

SUMMARY OF THE INVENTION

Therefore the object of this invention is to devise a microlens whichcan be produced especially in large-scale production with a radiantefficiency and brilliance as high as possible, which can be produced bya method as claimed in the invention and a device as claimed in theinvention in a simple manner which is suitable for large-scaleproduction with a flexible mold.

This object is achieved with the features of the claims. Advantageousdevelopments of the invention are given in the dependent claims. Allcombinations of at least two of the features given in the specification,the claims and/or the figures also fall within the framework of theinvention. At the given value ranges, values within the indicated limitswill also be disclosed as boundary values and will be claimed in anycombination.

The invention is based on the idea of producing a microlens by molding alens directly into the carrier wafer so that the carrier wafer does notobstruct the light beam passing through the lens or is located outsidethe beam path. Thus the lens is molded from two sides of the carrierwafer by an upper and a lower lens die so that a high precisionmicrolens can be produced by especially collinear alignment of the upperlens die to the lower lens die and/or to the carrier wafer. Deviatingfrom the existing procedure in the prior art makes it possible asclaimed in the invention to make the lens mold more flexible, especiallyin the region of the lower lens side which had been previously coveredby the carrier wafer.

The rigid carrier wafer provides for stability of shape in theproduction of the lens since it generally entails expansion/shrinkage ofthe lens.

In particular, in the simultaneous production of a plurality of lenseswith one carrier wafer matrix and two lens die matrices which is enabledby this method and the device as claimed in the invention, the carrierwafer ensures moreover the integrity of the optical axes of the lensesto one another. The respective grid positions of each correspondingupper and lower die and the corresponding opening of the carrier wafercan thus be exactly aligned since the carrier wafer is not subjected tochanges in size in production. With one carrier wafer matrix and the twocorresponding lens die matrices, at a carrier wafer diameter of 200 mmroughly 2000 lenses can be produced with one process run as claimed inthe invention.

As claimed in the invention, there is a microlens negative on each lensdie whose shape determines the curvature of the respective side of themicrolens produced with the method as claimed in the invention. Theshape of the lenses can be made convex, planar or concave. The lensprofile can be spherical or aspherical as claimed in the invention.

The lens is formed from UV-curable or thermally curable lens material,one of the two lens dies being made UV-transparent in the case of theUV-curable lens material. The lens material as claimed in the inventionis at least largely, preferably completely free of solvent and issuitable for complete crosslinking.

The carrier wafer which is provided as claimed in the invention and intowhich the lens can be molded or is molded, is used for holding andfixing of the lens in the microlens which has been produced as claimedin the invention and especially as spacer between the upper and thelower lens die so that among others the thickness of the microlens isinfluenced by the thickness of the carrier wafer. The carrier wafer canalso be advantageously used for producing a plurality of microlenses bymany lenses being molded into the carrier wafer and being divided laterinto individual microlenses. To the extent the carrier wafer is made asa ring with an opening for holding the lens, the lens is held andstabilized on its entire circumference by the carrier wafer. The lensring can be made square, semicircular, triangular, elliptical on itsinside and/or its outside, on the inner ring be advantageously a holdingstructure, especially projections, being designed for more effectivefixing of the lens in the carrier wafer, preferably as openings of thecarrier wafer, therefore in one piece with the carrier wafer. Preferablythe holding structures project over the inside of the ring by at leastone fifth of the thickness of the carrier wafer.

Alternatively the holding structure is made as surface roughness of theinner ring of the carrier wafer on which the lens material and the curedlenses are held in the direction of the optical axis.

To avoid thermal expansion or thermal stresses it is advantageouslyprovided that the lens material and the carrier wafer have a coefficientof thermal expansion of roughly the same magnitude. To the extent thelens and the carrier wafer have a different coefficient of thermalexpansion the lens as claimed in the invention is made such that theshape of the lens at different temperatures essentially scales so thatthe lens in different temperature states is self-similar and hardlychanges its optical properties. In this case it is advantageous if thelens as claimed in the invention has a greater coefficient of thermalexpansion in the cured state than the carrier wafer. In this way, in theproduction of the microlens a minimum empty space is formed between thecarrier wafer and the lens which is used as a buffer for the expansionof the lens at different temperatures in the production of the microlensdue to the larger coefficient of thermal expansion of the lens when thelens is cooled during production. As claimed in the invention in theproduction of the microlens, especially in a UV-curing lens materialthere can be heating during curing of the lens material in order toachieve the aforementioned effect.

Accordingly the lens as claimed in the invention is connected positivelyto the carrier wafer, especially to the inner ring of the carrier wafer.

The lens dies in one advantageous embodiment consist of a carriersubstrate and a microlens negative which is fixed on the carriersubstrate. According to one embodiment of the lens die at least one lensdie is provided with a drain for excess lens material.

The process for producing the microlens preferably proceeds as follows:

The microlens negative of the lower lens die is fixed, especially byfixing of the lens die by a receiving means for accommodating the lowerlens die. Then the carrier wafer is aligned/adjusted to the microlensnegative of the lower lens die such that the optical axis of themicrolens negative and the longitudinal center axis of the carrier waferare collinear. Alternatively and especially for production of severallenses simultaneously with a carrier wafer the carrier wafer is adjustedcoplanarly with the carrier substrate of the lower lens die. Then thecarrier wafer is placed and fixed on the carrier substrate of themicrolens negative, therefore on the lens die. Fixing is conceivable byvacuum structures in the lens die or electrostatically by electrostaticmeans machined into the lens die, but also mechanically by clampingand/or adhesion.

Then lens material, especially a UV-curable or thermoplastically curablepolymer, is introduced into the opening of the carrier wafer by way ofthe microlens negative of the lower lens die, the viscosity of the lensmaterial during introduction being chosen such that the lens spaceformed by the inner ring of the carrier wafer and the lens die can befilled free of bubbles. The amount of lens material added is such thatin subsequent embossing of the lens there is enough lens material tofill the microlens negative of the upper lens die.

In one alternative embodiment introduction takes place over the entiresurface on the carrier wafer/carrier wafer matrix, as a result of whichthe opening/openings is/are filled and excess lens material or lensmaterial which is needed for the lens structures which project over thecarrier wafer covers the carrier wafer/carrier wafer matrix.

According to another alternative embodiment of the invention, the lensmaterial is delivered individually into the opening(s) of the carrierwafer/carrier wafer matrix, especially by metering with a dropletdispenser or with a pipette.

Then the optical axis of the upper lens die is calibrated collinearlywith the optical axis of the lower lens die or the lens negative of thelower lens die and/or with the longitudinal center axis of the carrierwafer. Then the upper lens die is pressed with pressure onto the lowerlens die and the carrier wafer which is located in between. In the caseof UV curing the lens material is irradiated by means of UV light withrelatively high intensity through the upper lens die which in this caseis transparent or UV-permeable, and/or through the lower lens die, andthe polymer is crosslinked. In thermoplastic curing the material of thelens die is provided with relatively high thermal conductivity in orderto promote heat transport.

The alignment of the lens dies with the carrier wafer takes place by analignment mechanism, especially with an alignment precision of less than500 μm, especially less than 200 μm, preferably less than 100 μm,ideally less than 70 μm deviation and/or with optical alignment meanswith an alignment precision of less than 10 μm, especially less than 5μm, preferably less than 3 μm deviation. Optical alignment is especiallyadvantageous for the alignment of the upper and lower lens die or theupper and lower lens die matrix. Optical means are especially lasers ormicroscopes which enable exact alignment by markings on the lens dies oron the lens die matrices.

According to one especially preferred embodiment of the invention thelens die is aligned, especially in addition to the alignment on thecarrier wafer, by parallel alignment of the lens dies to one another,the position of the optical axis/axes of the lens negatives being takeninto account.

By the contact surfaces of the lens dies adjoining the correspondingmating surfaces of the carrier wafer for coplanar alignment of the lensdies during stamping, the lens dies are aligned using the especiallyparallel opposite mating surfaces of the carrier wafer, as a result ofwhich the optical axes of the lens negatives are exactly aligned.

As claimed in the invention a deviation of less than 10 μm over thewidth of each lens which is between 100 μm and 6 mm means parallel. Atmost the deviation of the parallelism is therefore 10%, especially lessthan 7%, preferably less than 5%, even more preferably less than 3%,ideally less than 1.5%. Thus essentially ideal agreement of the opticalaxes is enabled. The height of the lenses is conventionally between 50and 500 μm, and the height for the microlens as claimed in the inventioncompared to the prior art can be reduced essentially by the width of thecarrier wafer.

According to one embodiment of the invention, on the microlens,especially parallel to the optical axis of the lens, there is aself-centering structure, especially as an opening of the carrier wafer,which is used for example for automatic alignment of the microlens withanother microlens which has a corresponding, inverted structure,especially in the form of orientation ribs. The self-alignment worksaccording to the key-lock principle or in the manner of a tongue-ingroove joint. A cone-like configuration of the tongue-in-groove joint isespecially preferred.

The description of the method and of the device for producing anindividual microlens relates analogously to the production of aplurality of microlenses with the feature that it is enabled only by theconfiguration as claimed in the invention. Instead of an upper lens diean upper lens die matrix is used which comprises several lens dies,especially as a one-piece lens die structure. The lower lens die matrixis formed analogously. The carrier wafer as a carrier wafer matrix,especially in the form of a one-piece carrier wafer structure, isprovided with a plurality of openings.

For action in the preferred alternative in which the lens die matricesare aligned on the contact surfaces of the lens die matrices, thecarrier wafer matrix can be penetrated by a spacer of the upper and/orlower lens die matrix which forms the contact surface at the time anddictates the thickness of the lens.

According to one independent version of the invention, the carrier waferafter producing the microlens is at least partially, preferablycompletely removed. In this way the dimensions and the weight of thelens are further reduced. Removal takes place preferably by ejecting thelens from the carrier wafer which is provided especially with a holdingstructure with minor projections. Minor projections are made especiallyas surface roughness of the inner ring.

Other advantages, features and details of the invention will becomeapparent from the following description of preferred exemplaryembodiments and using the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross sectional view of a microlens matrix asclaimed in the invention consisting of a plurality of lenses molded intoa carrier wafer structure,

FIG. 2 shows a schematic of a device as claimed in the invention forproducing a microlens as claimed in the invention,

FIG. 3 shows a schematic of a microlens matrix as claimed in theinvention consisting of a plurality of lenses molded in a carrier waferstructure according to one alternative embodiment,

FIG. 4 shows a schematic of a device as claimed in the invention forproducing a microlens as claimed in the invention according to onealternative embodiment,

FIG. 5 shows a schematic of shapes of a holding structure as claimed inthe invention, and

FIG. 6 shows a schematic of a device as claimed in the invention forproducing a plurality of microlenses.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the figures the same parts and parts with the same function arelabeled with the same reference numbers.

FIG. 1 shows a microlens matrix 31 in cross section which consists of acarrier wafer structure 32 and a plurality of lenses 14 molded intoopenings 2 of the carrier wafer structure 32 or the later carrier wafer17. The microlens matrix 31 can be separated by known cutting methodsinto individual microlenses 1, as is shown isolated in the explodedrepresentation in FIG. 2.

The microlenses 1 can be produced as microlens matrix 31 in large-scaleproduction, but can also be produced individually. FIG. 2 schematicallyshows production using an individual microlens 1.

As shown in FIG. 2, a lower lens die 18 consisting of a carriersubstrate 21 and a lens mold 20 which has been fixed, especiallycemented, on the carrier substrate 21 can be accommodated on receivingmeans of the device as claimed in the invention which are not shown. Inlarge-scale production on the carrier substrate 21 there can be aplurality of lens molds 20 or one lens mold 20 with a plurality of lensnegatives 19, the lens negatives 19 or the lens molds 20 being appliedto the carrier substrate 21 such that they can be aligned flush with theopenings 2 which are shown in FIG. 1.

The lens negative 19 is surrounded by a contact surface 22 which islocated orthogonally to the optical axis of the lens negative 19 and onwhich the carrier wafer 17 comes into contact with a correspondingmating surface 23 which is annular in this exemplary embodiment, forminga seal.

As soon as the carrier wafer 17, as shown in FIG. 2, is aligned with itslongitudinal center axis to the optical axis A, the carrier wafer 17with its mating surface 23 is fixed on the contact surface 22 so that aninner ring 16 of the carrier wafer 17 and the lens mold 20 form a lensspace 3 into which the lens material which forms the lens 14 can beintroduced via delivery means. After delivering the lens material intothe lens space 3 the lens 14 is stamped as described below.

For this purpose an upper lens die 9 which is provided by receivingmeans for accommodating an upper lens die 9 can be aligned by alignmentmeans for alignment of the upper lens die 9 with the opening 14 and/orthe lower lens die 18, especially to the optical axis A of a lensnegative 12 of a lens mold 11 applied on a carrier substrate 10. Theupper lens die 9 is formed analogously to the lower lens die 18 and hasa contact surface 8 for especially sealing contact of the upper lens die9 with one mating surface 7 of the carrier wafer 17. The mating surface7 is located opposite the mating surface 23 and parallel to it.

After alignment of the upper lens die 9, the upper lens die 9 is loweredalong the optical axis A onto the carrier wafer 17 and subjected topressure, the corresponding counter pressure being applied via the lowerlens die 18. The lens material fills the lens space 3 without bubblesand possible excess lens material can drain or be sucked out of the lensspace 3 via a drain system which is not shown in the figures.

According to one preferred embodiment of the invention the lens materialcan be optimally subjected to pressure when a vacuum, especially with apressure <500 mbar, preferably <300 mbar, even more preferably < than200 mbar, ideally <100 mbar, is applied by vacuum means at the same timein the opening, especially between the upper lens die and the carrierwafer.

According to one still more preferred embodiment the vacuum duringpressurization is <70 mbar, especially <40 mbar, preferably <15 mbar,even more preferably <5 mbar.

The lens material is cured via curing means of the device so that a hardlens 14 is formed which corresponds to the shape according to the lensspace 3. The curing means can be a light source for UV light forUV-curable lens material or heating means for thermoplastically curablepolymer as lens material.

By the carrier wafer 17 which has the inner ring 16 and an outer ring 24having a holding structure 25 in the form of a projection which projectssharply in the direction of the optical axis A of the inner ring 16 inthe illustrated exemplary embodiment as shown in FIG. 2, the lens 14 andthe carrier wafer 17 form a positive connection which cannot benondestructively broken. As shown in FIG. 2, holding structure 25extends from inner ring 16 at a location spaced from mating surfaces 7,23 of carrier wafer 17. As such, holding structure 25 projects into anouter peripheral portion of lens 14.

Alternative shapes of the holding structure 25 are shown in FIG. 5. Thealternative embodiment shown in FIGS. 3 and 4 corresponds, with thedifference that the lens 14′ in the exemplary embodiment shown hereacquires a different shape, to the exemplary embodiment of the inventionshown in FIGS. 1 and 2. Other changes of shape without functionalchanges relate to the lens 1′, the upper carrier wafer 9′ and the lowercarrier wafer 18′. Reference is made to the explanation for FIGS. 1 and2 as well as 5.

FIG. 6 shows a device for executing the method as claimed in theinvention with receiving means 50 for accommodating the upper lens diematrix 4 which has a plurality of upper lens dies 9, 9′ and receivingmeans 51 for accommodating the lower lens die matrix 5 which has aplurality of lower lens dies 18, 18′. The receiving means 50, 51 eachconsist of a chuck 52, 53 and one die holder 54, 55 which is U-shaped incross section and which is attached to the respective chuck 52, 53 forexample via vacuum paths (not shown).

The upper and/or the lower receiving means 50, 51 can be moved up anddown by a control which is not shown.

On the lower lens die matrix 5 there are alignment means 56 foralignment of the lower lens die matrix 5. On the upper lens die matrix 4there are alignment means 57 for alignment of the upper lens die matrix4. On the carrier wafer matrix 32 there are alignment means 58 foralignment of the carrier wafer matrix 32.

The alignment means 56, 57 and/or 58 comprise at least one opticalsystem (not shown) and are controlled by a control unit which is notshown. Furthermore the alignment means 56, 57 and/or 58 comprisemovement means for moving the receiving means 50 and/or 51 parallel tothe carrier wafer matrix 32.

On the lower receiving means 51 there are fixing means 59 for fixing thecarrier wafer matrix 32 with the lower lens die matrix 5 after alignmentby the alignment means 56.

Furthermore, there is delivery means 60 in the form of an injectionmeans 61 with an especially interchangeable injector 62 which isconnected to a storage tank for the lens material via a flexible fluidline 62. The injection means 61 is made as a drop dispenser and canapproach each opening 2 of the carrier wafer structure and add a givenamount of lens material to it.

Stamping means for applying pressure apply an adjustable superficialforce along the carrier wafer matrix, especially by forces Fo and Fuwhich are applied to the alignment means 50, 51 and which act oppositelyin the direction of the carrier wafer matrix, for example transferringthe force by one hydraulic cylinder at a time.

Furthermore the device comprises means for curing of the lens materialduring stamping, especially a UV light source and/or heating means whichacts on the lens material.

The invention claimed is:
 1. Method for producing a microlens with acarrier wafer, the carrier wafer having an inner ring extending betweenopposite facing surfaces of the carrier wafer, the inner ring definingan opening of the carrier wafer for accommodating the microlens therein,wherein a holding structure extends from an annular surface of the innerring at a location spaced from both of the opposite facing surfaces ofthe carrier wafer, the method comprising a step of: molding themicrolens into the carrier wafer by stamping of the microlens using twolens dies each having a contact surface dimensioned to adjoin acorresponding mating surface of the carrier wafer for coplanar alignmentof the lens dies during stamping, and wherein the holding structureprojects into an outer peripheral portion of the microlens for positivefixing of the microlens to the inner ring of the carrier wafer such thatthe microlens is fixed to the holding structure and wherein the carrierwafer and the microlens form a positive connection that cannot benondestructively broken.
 2. Method as claimed in claim 1, wherein thecarrier wafer is located outside a beam path of the microlens.
 3. Methodas claimed in claim 1, wherein each of a plurality of microlenses ismolded into a corresponding opening of a carrier wafer matrix whichencompasses corresponding carrier wafers during stamping.
 4. Method asclaimed in claim 1 with the following sequence: alignment and fixing ofa lower lens die with the opening of the carrier wafer, delivery of alens material which forms the microlens into the opening, stamping ofthe microlens by acting on the lens material with an upper lens die andcuring of the microlens.
 5. A method of forming a microlens, comprisingthe steps of: providing a carrier wafer having an annular holdingstructure that defines a portion of an opening, said opening dimensionedto accommodate a microlens therein with space between said microlens andsaid holding structure, wherein said annular holding structure is spacedfrom opposite facing surfaces of said carrier wafer; and integrallyforming a microlens and a peripheral portion by a stamping process usingtwo lens dies, said microlens being formed in said opening and saidholding structure projecting into said peripheral portion, wherein saidmicrolens is supported and stabilized on its entire circumference bysaid peripheral portion being attached to said holding structure whereinthe carrier wafer and the microlens form a positive connection thatcannot be nondestructively broken and wherein at least one of the lensdies includes a drain hole for conveying excess lens material from saidmicrolens during the stamping process.
 6. Method as claimed in claim 1,wherein the holding structure is an annular projection extending fromthe annular surface of the inner ring.
 7. Method as claimed in claim 6,wherein the annular projection is square-shaped or triangular-shaped. 8.Method as claimed in claim 1, wherein the holding structure is aplurality of projections extending from the annular surface of the innerring.